Coronary angioplasty has gained wide acceptance as an alternative to open heart coronary bypass surgery for treatment of acute and chronic heart problems. A major contributory factor in such heart problems is a reduction in the nutrient blood flow to muscles of the heart which results from a reduction of blood flow through the coronary blood vessels. This reduction in flow may be caused by atherosclerotic plaque deposits on the walls of the affected blood vessels, which causes a narrowing of the lumen or channel of the blood vessel, referred to as a stenosis. This narrowing of the lumen has detrimental effects on the rate of blood flow therethrough which may cause the formation of a thrombosis or clot to occur.
The most common form of angioplasty is percutaneous translumenal coronary angioplasty (PTCA) which utilizes a catheter having an inflatable balloon at its distal end. These catheters are interchangeably referred to as dilatation, perfusion, angioplasty, PTCA or balloon catheters. The physician using fluoroscopy, guides the wire and/or the catheter through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying fluid under pressure through an inflation lumen to the balloon. The inflation of the balloon opens the blood vessel to re-establish acceptable blood flow through the blood vessel.
When the balloon is inflated during typical angioplasty procedures, all blood flow through the blood vessel is blocked. It is believed that long term inflation of the stenosis will increase the probability that the stenosis may remain open after dilation thereby reducing the risk of restenosis. Also, longer inflations often result in smoother molded luminal results, may decrease vessel trauma, and long inflations are currently used to repair injury caused by shorter inflation times during angioplasty procedures. However, typical dilation times range from about 30 to 60 seconds because longer inflation periods may result in dangerous ischemic conditions in areas distal to the inflated balloon in a blood vessel. This ischemic condition may be indicated by ST segment changes and dramatic increases in patient discomfort as well as a decrease in blood pressure. There is a belief that the restenosis rate can be lowered if longer inflation time is utilized for inflating the balloon while in a stenosis to reduce patient discomfort so that the stenosis will remain open and not restenose. To accomplish longer inflation times, there is a need to provide sufficient blood flow to the portions of the heart distal of the stenosis during inflation.
Several approaches have been adopted in an attempt to address the problem of maintaining blood flow and hence preventing ischemia and ST segment changes during prolonged dilatations. Initial attempts to overcome this problem relied on passive perfusion catheters. Passive perfusion catheters which have been proposed in the past have utilized at least one opening in the guide catheter and/or the dilatation catheter both immediately proximal and distal to the inflated balloon. However, initial attempts at passive perfusion often resulted in sub-optimal blood flow through the dilatation catheter. Several attempts have been made to overcome this sub-optimal blood flow. Examples of such attempts may be seen in U.S. Pat. Nos. 4,661,094 to Simpson, 4,877,031 to Conway et al., 5,087,247 to Horn et al., and 4,790,315 to Mueller, Jr., et al.
In each of the above-referenced patents, attempts were made to vary either the size or shape of the openings, vary their spacing and location relative to each other and about the guide catheter and/or dilatation catheter. Varying the size, shape, location and spacing of the openings has done little to overcome the problem of sub-optimal flow associated with passive perfusion.
Active perfusion has been attempted to overcome the problem of maintaining sufficient blood flow during extended periods of dilatation which known attempts at passive perfusion have been unable to solve. Active perfusion utilizes a mechanical pump to force blood and/or other fluid through the balloon catheter.
Original attempts at active perfusion required withdrawing the blood from apertures at an upstream location and delivering the blood to the pump itself and to processing stations located ex vivo, and then returning it to the catheter to be expelled back into the blood vessels and apertures located downstream of the intake apertures. Examples of such an approach may be found in U.S. Pat. No. 5,137,513 to McInnes et al., and U.S. Pat. No. 5,158,540 to Wijay et al. An alternative approach was to provide a perfusion catheter and pump arrangement wherein the blood or other body fluid was drawn into the catheter, bypassing the obstruction, and then immediately expelling the blood under pressure, without undergoing an ex vivo loop. An example of this approach may be seen in U.S. Pat. No. 4,857,054 to Helfer.
Regardless of the approach, all forms of active perfusion require some form of mechanical pump which necessitates additional equipment thereby complicating the angioplasty procedure. In addition, pumping blood up to high pressures has a potential effect of causing hemolysis.
The present invention incorporates many of the known benefits of both active and passive perfusion while improving the passive perfusion catheters.